1. Field of the Invention
The invention relates to a ground working machine and a method, respectively, for working ground surfaces or traffic surfaces, in particular a cold recycler or soil stabilizer as a self-propelled machine or attachment unit.
2. Description of the Prior Art
Such ground working machines are used for the processing of materials, namely, for example, the stabilization of soils of insufficient load-bearing capacity, the pulverization of asphalt pavements and the recycling of bound or unbound pavement surfaces. For the improvement or stabilization of soils, it is known to introduce a powdered or liquid binding agent into the soil in order to increase the suitability for placing and the load-bearing capacity of said soil. The known ground working machines comprise a milling/mixing drum revolving in a mixing chamber, said milling/mixing drum being arranged, in a height-adjustable fashion, below a drum housing enclosing the milling/mixing drum and attached to the machine frame. The ground working machine may be self-propelled or be an attachment unit. Examples of such machines are described in WO 96/24725 (U.S. Pat. No. 5,893,677), WO 2005/054578 (U.S. Pat. No. 7,918,512) or EP 2218823 A (U.S. Pat. No. 8,511,933).
Reference is made to these earlier patent applications regarding the description of the individual components of such ground working machine.
The required processes, such as crushing of the ground material, addition of binding agents, mixing and spreading of added materials, are performed, in a fashion adapted to the respective application, in the mixing chamber located between the drum housing and milling device.
In a known ground working machine as it is depicted, for example, in FIG. 1, it is already known to provide front and rear pivotable drum flaps at the drum housing in order to limit the escape of the milled-off material or material to be mixed and/or to be crushed, respectively, during the working process. In this design, the position of the drum flaps depends on the task or the nature of the subsoil and the desired work result, respectively. It is thus possible, for example, to influence the grading curve, that is, the size distribution of the milled-off pieces of material, by means of the position of the front drum flap as seen in working direction. In the process, the adjustment of the drum flaps is effected in a pivoting movement about a pivoting axis extending transverse to the working direction and parallel to the axis of the milling/mixing drum.
It is of disadvantage in the mentioned state of the art that, as a result of the layer structure of the ground or traffic surface, the milling/mixing drum can break slabs out of the surface course in particular when operating against the direction of travel in which the milling/mixing drum rotates in opposite direction to the direction of rotation of the wheels or track units.
This is of disadvantage in particular because crushing the existing road pavement according to specification is made more difficult and, in the process, some oversized fragments enter the milled material contained in the mixing chamber so that the size distribution of the milled fragments is inhomogeneous and does not correspond to the specified grain size distribution.
Furthermore, large fragments that are caught by the milling drum can exert unwanted forces on the milling/mixing drum or on the drum housing. In the process, damage may be caused or reactions of the ground working machine generated which rock or lift the machine so that the working process is disturbed and the quality of the work result is impaired.
It is already known from WO 2012/062456 (US 2013/322963) to arrange crusher bars inside the drum housing. The disadvantage is that an additional design effort is required inside the milling drum housing and maintenance of the crusher bar elements is difficult and time-consuming due to the confined space inside the drum housing. In addition, a build-up of the milled material occurs in the mixing chamber so that increased performance is required for the operation of the milling/mixing rotor or the milling process can be performed at a slower operating speed only. Arranging the crusher bar on the inside leads to larger fragments and slabs being hurled against the crusher bar inside the drum housing again and again until they are crushed to such an extent that they can pass through the gap between the milling/mixing rotor and the drum housing. In the process, a build-up of the milled material easily forms which requires the milling/mixing drum to operate with significantly increased resistance.
According to the state of the art, the pivoting angle of the front drum flap is adjustable manually by the machine operator and remains essentially constant for the entire working process. In this arrangement, the drum flap does usually not rest on the ground.